3.5. Biological Theories of Personality

The biological theory of personality posits that part of who we are comes from biology and the genes we inherit from our parents.
Example: children may show certain behaviors because they share similar genes with their parents.
Viewpoint nuance: not all psychologists fully agree, but research indicates biology plays an important role in shaping personality (Khatibi & Khormaee, 2016).

Challenge: it's difficult to separate genetic influence from environmental influence.
Adoption studies: look at children raised apart from their biological parents to see whether traits like personality or disorders (e.g., alcoholism) are inherited.
Twin studies: compare identical or fraternal twins, sometimes raised in different homes, to separate genetics from environment (Plomin et al., 2013).
Why useful:
- Identical twins share the exact same genes; they are often studied to gauge biology's impact on personality.
- Research shows genetics play a stronger role in shaping personality than the environment on average.
Evidence highlights:
- Identical twins (monozygotic, MZ) usually show more trait similarity than fraternal twins (dizygotic, DZ).
- DZ twins share about half their genes, i.e., ext{genetic similarity}{DZ} \approx \tfrac{1}{2}, while MZ twins share essentially all their genes, i.e., \text{genetic similarity}{MZ} = 1.
- Identical twins raised in the same home tend to develop very similar habits and behaviors.
Key references: Cadoret (1995); Plomin et al. (2013); Polderman et al. (2015).

Core idea: genes and environment work together to shape personality.
Upbringing and situational context influence how traits are expressed and refined.
Interaction example: a person may inherit certain tendencies from their parents, but environmental factors can encourage, attenuate, or adapt these traits to fit social contexts.
Foundational stance: nature and nurture are interdependent, and their effects are integrated rather than isolated (Krueger et al., 2008).

The brain and its activity are central to personality.
Brain areas and neural networks contribute to personality traits through patterns of activity and connectivity.
Neurotransmitters implicated in mood, motivation, and behavior include dopamine and serotonin.
The biological perspective connects personality traits to brain activity and neurochemical processes.
Foundational theorists linking brain function to personality include Eysenck, Allport, and Cattell.
Supporting references: DeYoung (2013); Fischer et al. (2018).

Core idea: individuals differ in how strongly their brains react to rewards and punishments.
These differences help explain variations in anxiety, impulsivity, and susceptibility to certain mental health problems (Gray, 1970, 1982).
Gray built the theory by adapting animal learning research to human personality, proposing three brain systems that respond differently to positive or negative experiences.
Three main systems (as summarized in RST):
- Fight-Flight-Freeze System (FFFS): responsivity to fear; leads to avoidance or escape of dangerous situations; higher sensitivity linked to fear-prone or risk-avoidant behavior.
- Behavioral Inhibition System (BIS): responsivity to anxiety and conflicting cues; leads to caution and hesitancy; individuals high in BIS tend to worry more and be very careful.
- Behavioral Approach System (BAS): responsivity to rewards; drives approach toward rewarding or exciting stimuli; associated with impulsivity and optimism.
Summary of RST impact: the interplay of FFFS, BIS, and BAS shapes daily behavior and potential psychopathology.
Key references: Gray (1970, 1982); DeYoung (2013); Fischer et al. (2018).

The biological view integrates genetics, brain function, and neurochemistry to explain personality differences.
It supports the idea that some traits have a heritable basis, yet environmental context and learning experiences modulate how these traits are expressed.
Practical implications include understanding vulnerability to certain disorders (e.g., anxiety, impulsivity-related conditions) and recognizing how environments can influence trait development.
Ethical and philosophical considerations include the balance between recognizing genetic influences and avoiding determinism, as well as the importance of creating environments that promote healthy personality development.

Genetics and personality links: Khatibi & Khormaee (2016); Plomin et al. (2013); Cadoret (1995); Polderman et al. (2015).
Nature–nurture integration: Krueger et al. (2008).
Brain and personality: DeYoung (2013); Fischer et al. (2018); Eysenck, Allport, Cattell.
RST and Gray: Gray (1970, 1982); additional elaboration by related reviews.

Important numerical notes:

Identical (monozygotic) twins share essentially 1 (100%) of their genes.
Fraternal (dizygotic) twins share about \tfrac{1}{2} (50%) of their genes.
Three main brain systems in Gray’s Reinforcement Sensitivity Theory: FFFS, BIS, BAS.